Improvement of the surface quality of an automotive member by a modification of the stamping tool

This paper concerns a design modification of the stamping die for the upper member of a front end module (FEM) carrier of an auto-body made of high strength steel in order to improve the surface quality of the stamped product. A small inferiority caused by wrinkling at the sidewall of the member has been observed after the draw-forming stage. A finite element analysis of the whole geometry is pursued in order to fully accommodate the complicated shape. The analysis focuses on the contact condition between the tools and the blank sheet in order to inspect problems in the metal flow of the drawn part. Simulation with the initial design shows that the excess metal is developed by the irregular contact of the blank and tools, which remains after the final stroke. This paper proposes three guidelines for the tool modification. The first is to increase the blank holding force; the second is to add a draw-bead at the binder surface near the critical region in order to increase the draw-in force; the third is to modify the tool shape such as embossing at the wall in order to absorb the excess metal before the final stroke. The result of simulation with the modified design fully demonstrates that some of the proposed guidelines eliminate the surface defect and guarantee an improved surface quality.